NEW PATIO PROBLEM

[1Roger2]

I have a 12 month old patio which has developed this issue:

1: Numerous slabs appear not to have adhered to the mortar below, when tapped they sound hollow. I have lifted one and confirmed this, the mortar itself has set correctly and has a flat profile to match the slab.
The base was correctly prepared with compacted hard core and then a 75mm mortar base for the slabs.
The builder is coming back to rectify - what is the recommended action that he should carry out. Is it essential that the slabs stick to the mortar below if the mortar and pointing are sound?
2: The pointing is separating around some slab edges and weak around others.
My recollection is that the weather was quite warm during some of the slab laying.
Glad for any advice.

 

[wrathkeg]

http://www.pavingexpert.com/repair.htm

 

[r896neo]

firstly 75mm is a bit deep for a mortar bed. 25-50mm is more like it.

As for adhesion it is not strictly necessary in theory. but you may get frost problems if water gets between and under the slabs.

Pointing coming loose is a sure sign of either crap pointing mix or more usually slight movement of the slab.

It sounds like its bedded well if you lifted one and it had a nice flat full bed so i suppose the pointing is the only issue to be sorted.

Pointing in very warm weather often lets it dry out too quickly which may have been the probloem. I'd very carefully check that affected areas are not moving at all though.